1. Field of the Invention
This invention relates to an apparatus for forming a film, and more specifically to a film-forming apparatus which is adapted to produce an insulating film, for example, by the CVD (chemical vapor deposition) method using an activated reaction gas.
2. Description of the Prior Art
In the manufacture of semiconductor devices, CVD devices are useful for the formation of SiO.sub.2 film, PSG film, BSG film, BPSG film, Si.sub.3 N.sub.4 film, amorphous Si film, polycrystalline Si film, W film, Mo film, WSi.sub.2 film, MoSi.sub.2 film, and Al film.
The conventional CVD devices are classified, in accordance with the means employed to activate the reaction gas, into the following three main types:
(1) Thermal CVD devices PA1 (2) Photo-assisted CVD devices PA1 (3) Plasma enhanced CVD devices
The thermal CVD devices are provided with heating means for heating a reaction gas thereby imparting thermal energy to the reaction gas and activating it and maybe further classified by the pressure used, as either the low pressure type or the atmospheric pressure type. Also, according to the temperature of the substrate, they are classified as either the low or high temperature type. Further, in accordance with the means of heating, they are classified as resistance heating, induction heating, or lamp heating type. In accordance with location of installation of the heating means, they are classified as either a hot wall or a cold wall type.
The photo-assisted CVD devices are furnished with light emitting means for irradiating a reaction gas with ultraviolet light to impart light energy to the reaction gas and to thereby activate it and are capable of forming a film under low or high pressure, at a low temperature.
The plasma enhanced CVD devices have plasma-forming means for directly or indirectly activating a reaction gas by means of AC electric power or a magnetic field and are generally operated under a low pressure and at a low temperature. Conventional types of plasma-forming apparatus include the parallel plate type for directly activating a reaction gas by irradiation with high frequency energy and the ECR type for indirectly activating a reaction gas by means of electrons to which energy has been imparted by high frequency electric power and a magnetic field.
Film-forming with a thermal CVD device at times proves undesirable because the substrate is heated to a high temperature. Further, it is in need of improvement in providing qualities such as film density.
The method for forming a film by the photo-assisted CVD device produces the film on surfaces extraneous to the substrate and gives rise to formation of particles. Further, it has such a low deposition rate as to necessitate improvement for actual use.
The method for forming a film by the plasma enhanced CVD device, particularly the parallel plate type, entails irradiation of a substrate with the plasma which creates a possibility of damage to the substrate. In cases where the damage to the substrate poses a particular problem, the plasma enhanced CVD method of the ECR type is adopted instead. This method is indeed effective in precluding damage to the substrate and in formation of a film of high density. Since it uses an extremely high frequency, on the order of 2.45 GHz, the device used by this method is inevitably very large.
Particularly, in the plasma enhanced CVD device, the shape of the inlet pipe for the film-forming gas and the location of the gas discharge orifice inside the chamber constitute important factors from the viewpoint of heightening the efficiency of plasma formation or improving uniformity of the film thickness and otherwise enhancing the uniformity of the film.